Mercury methylmercury

Alkyl mercury compounds in the blood stream are found mainly in the blood cehs, and only to a smah extent in the plasma. This is probably the result of the greater stabhity of the alkyl mercuric compounds, as well as their pecuflar solubiUty characteristics. Alkyl mercury compounds affect the central nervous system and accumulate in the brain (17,18). Elimination of alkyl mercury compounds from the body is somewhat slower than that of inorganic mercury compounds and the aryl and alkoxy mercurials. Methylmercury is eliminated from humans at a rate indicating a half-life of 50—60 d (19) inorganic mercurials leave the body according to a half-life pattern of 30—60 d (20). Elimination rates are dependent not only on the nature of the compound but also on the dosage, method of intake, and the rate of intake (21,22). 

Keywords Aquatic organisms, Chlor-alkali plants, Crayfish, Fish, Mercury, Methylmercury, Zebra mussel... 

Toimela TA, Tahti H. 1995. Effects of mercury, methylmercury and aluminum on glial fibrillary acidic protein expression in rat cerebellar astrocyte cultures. Toxicol in Vitro 9 317-325. 

Environmental Mercury Mercury/methylmercury Reverse phase Problems reported Harrington and Catterick (1997)... 

Lawson, N.M., R.P. Mason, and J.-M. Laporte. 2001. The fate and transport of mercury, methylmercury, and other trace metals in Chesapeake Bay tributaries. Water Res. 35 501-515. 

Inza, B., F. Ribeyre, R. Maury-Brachet, and A. Boudou. 1997. Tissue distribution of inorganic mercury, methylmercury and cadmium in the Asiatic clam (Corbicula fluminea) in relation to the contamination levels of the water column and sediment. Chemosphere 35 2817-2836. 

With respect to distribution in the body, the methylmercury species behave more like mercury metal, Hg(0), than inorganic mercury(II), Hg2+. Like elemental mercury, methylmercury compounds traverse the blood-brain barrier and affect the central nervous system. However, the psychopatho-logical effects of methylmercury compounds (laughing, crying, impaired intellectual abilities) are different from those of elemental mercury (irritability, shyness). 

Lawson N. M. and Mason R. P. (2001) Concentration of mercury, methylmercury, cadmium, lead, arsenic, and selenium in the rain and stream water of two contrasting watersheds in western Maryland. Water Res. 35(17), 4039-4052. 

The existence of the blood-brain barrier does not preclude the passage of chemicals into the brain. As is the case with all other cellular membranes in the body, lipid-soluble nonionized chemicals enter the brain by passive diffusion. Anesthetics, ethanol, and CNS depressants, for instance, rapidly diffuse into the brain in a matter of a few seconds or minutes. They also exit the brain rapidly when the concentration gradient between blood and brain is reversed. Elemental mercury, methylmercury, and tetraethyl lead are examples of lipid-soluble forms of metals that easily enter the brain, while the ionized, much less lipid-soluble inorganic salts of mercury and lead penetrate only poorly. 

See also Chlordane DDT (Dichlorodiphenyltrichloro-ethane) Dioxins Food and Drug Administration, US Mercury Methylmercury Polychlorinated Biphenyls (PCBs). 

Methylmercury is rapidly and nearly completely absorbed from the gastrointestinal tract 90-100% absorption is estimated. Methylmercury is somewhat lipophilic, allowing it to pass through lipid membranes of cells and facilitating its distribution to all tissues, and it binds readily to proteins. Methylmercury binds to amino acids in fish muscle tissue. The highest methylmercury levels in humans generally are found in the kidneys. Methylmercury in the body is considered to be relatively stable and is only slowly transformed to other forms of mercury. Methylmercury readily crosses the placental and blood/brain barriers. Its estimated half-life in the human body ranges from 44 to 80 days. Excretion of methylmercury is via the feces, urine, and breast milk. Methylmercury is also distributed to human hair and to the fur and feathers of wildlife measurement of mercury in hair and these other tissues has served as a useful biomonitor of contamination levels. 

Organic Mercury. Distribution of organic mercury compounds in humans and animals is similar to that of metallic mercury. Methylmercury distributes readily to all tissues, including the brain and fetus, after absorption from the gastrointestinal tract. The uniform tissue distribution is due to methylmercury s ability to cross diffusion barriers and penetrate all membranes without difficulty (Aberg et al. 1969 Miettinen 1973). Thus, tissue concentrations tend to remain constant relative to blood levels. About 90% of the methylmercury in blood is found in the red blood cells (Kershaw et al. 1980). The mean mercury concentrations in red blood cells were 27.5 ng/g and 20.4 ng/g in males and females, respectively, exposed to mercury, primarily from mercury-contaminated fish (Sakamoto et al. 1991). Because of this uniform distribution in tissues, blood levels are a good indicator of tissue concentrations independent of dose (Nordberg 1976). 

Medium or trophic level Methylmercury Inorganic mercury % Methylmercury... 

Yuan Y, Atchison WD. 1994. Comparative effects of inorganic divalent mercury, methylmercury and phenylmercury on membrane excitability and synaptic transmission of cal neurons in hippocampal slices of the rat. Neurotoxicology 15(2) 403-411. 

Precautions have always been practiced to contain the mercury (Table 8.3) of the operating mercury cells, primarily for the value of the metal itself. The steel flasks of the metal are also covered with a layer of water to reduce mercury vapor loss during shipping and storage. However, in 1970, it was demonstrated that mercury ions and the free metal could be converted by natural processes to the far more toxic forms of mercury, methylmercury salts and dimethyl mercury even under water [23, 24]. Industrialists, toxicologists, and legislators alike were alarmed by this discovery, which led to the rapid installation of control measures to drastically reduce mercury loss rates in Europe, Japan, and North America [25] (Table 8.4). 

Keywords mercury methylmercury speciation sediments estuaries lagoons 1. Introduction... 

May, K., Stoeppler, M., and Reisinger, K., Studies in the Ratio Total Mercury/Methylmercury in the Aquatic Food Chain, in Carcinogenic and Mutagenic Metal Compounds 2, Merian, E., Frei, R.W., Hardi, W., and Schlatter, C., (Eds.), Gordon and Breach Science Publishers, New York, 1987, pp. 109-115. 

Horvat, M., Zvonarid, T., Stegnar, P., Prosenc, A., Konda, D., Sabadin, A., Relation between total mercury, methylmercury and selenium in fish muscle from the Adriatic sea , in Heavy Metals in the Environment, Vol. I, Vemet, J-P, (Ed.), Edinburgh, CEP Consultants Ltd., 1993, pp. 370-313. 

May K, Stoeppler M and Reisinger K (1987) Studies in the ratio total mercury/methylmercury in the aquatic food chain. Toxicol Environ Chem 13 153-159. 

Additional research is recommended on inorganic mercury-Ugand formation in water and runoff and its effects on methylmercury formation in soils, and on quantification of the sources and transport characteristics of methylmercury in terrestrial environments. The mercury-Ugand form exiting the terrestrial watershed wiU strongly influence the mercury/methylmercury bioaccumulation potential in surface waters. Accordingly, more analyses are needed to determine the mercury... 

Mean mercury concentrations in organs of Minamata Disease victims dying between 1973 and 1985 remained elevated over those of residents not afflicted with Minamata Disease and dying between 1973 and 1991. Minamata Disease victims always had mean total mercury (methylmercury) concentrations, in mg/kg FW, >1.51 (().05) in kidney, >0.48 (0.035) in liver, >0.10 (0.016) in brain cerebmm, and 0.05 (0.026) in brain cerebellum. 

In contrast to the infiuence of inorganic mercury, methylmercury has only minor effects upon GSH-Px activity (Whanger, 1981). Methylmercury had no significant effect upon GSH-Px in the testes, and only those rats fed 25 ppm methylmercury had significantly lower GSH-Px activity in erythrocytes, kidneys, brain, and livers. Additions of 7.5 or 15 ppm methylmercury to the diet had no significant effect on the activity of this enzyme in any of these tissues. The slight reduction in GSH-Px activity... 

Biomagnification of mercury. Methylmercury compounds emitted from industry find their way to rivers and lakes where they are absorbed by krill and small aquatic organisms. These are then eaten by small fish, which in turn are eaten by larger fish. Since mercury is only slowly removed from the organism s body, the levels of mercury increase inside the cells of the organism, until at the top of the food chain - humans - the level is... 

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